1. Field of the Invention
The present invention relates generally to the fabrication and assembling of building frame components and, more particularly, to devices for accomplishing this. Specifically, the present invention relates to apparatus for the efficient and precise formation of metal frame components to enable easy assembly and use of the same in both commercial and residential structures.
2. Description of the Prior Art
In general, wall structures for both residential and commercial construction have been made over the years using the so-called stick framing method and construction. In such stick frame construction, the structural walls are made from wood studs, and the top and bottom wood framing members are called plates. Typically, the studs and plates are made from two-by-four lumber members which are generally 2″ in thickness and 4″ in width cut to the desired length. Stick framing generally involves the technique of nailing the studs to the top and bottom plates and are normally spaced 16″ on center to form a building structural wall. Systems for arranging these components into wall structures are illustrated in U.S. Pat. Nos. 3,986,247, 4,876,787 and 5,646,860.
In recent years, high-rise and other commercial building structures have replaced standard stick frame construction with steel structures. High-rise buildings typically employ straight column members subjected to high axial compression forces. The use of solid or rectangular rolled-steel sections typically in the form of steel studs supported between steel tracks has now become the standard construction format for commercial wall construction. Such steel members can be produced economically in a wide range of sizes and are readily assembled into wall and window sections. Examples of such devices are illustrated in U.S. Pat. Nos. 3,877,129 and 4,078,288.
Light gauge steel framing has been available to the construction market for well over forty years now. In fact, it has become the dominant, i.e. greater than 90 percent, construction technique in the commercial industry. However, wood is still the dominant framing material in the residential construction field, still amounting to about 85-92 percent. Considerable time and money has been expended by numerous trade and industry organizations, particularly during the past ten or twelve years, in study and research to determine why there is this vast difference in usage between these two construction fields, which at first glance would appear to have equal need and use for this material in their respective construction fields. As a result of the above findings, it has been determined that there has been noticeable progress made by light gauge steel framing in gaining a larger portion of the residential building market. Nonetheless, this progress has been a slow, moderate increase as opposed to the extreme dominance of steel framing vs. wood stick framing which has occurred in the commercial construction field.
There are a number of reasons for this disparity of usage of steel framing between these two fields of construction. Among the obstacles faced are traditional residential construction approaches as well as production methods for steel framing components. The production method of choice for producing light gauge steel framing has been, and will most likely continue to be, cold roll forming. This is due to its inherent low production cost with almost no material scrap loss factors. During the last 50 years, cold roll forming of steel has gone from substantially a “black art” with machines and materials which required considerable operator experience and skill, to a production technology which today is performed by higher precision machines and with fewer operator skills while using materials that are much more uniform in quality.
There are two main components used in light gauge metal framing. These components include studs (similar to wood framing) which in walls are the vertical members, and tracks, which are the top and bottom horizontal frame members to which the studs are attached. Both components are basically a U-shape component with the studs having inwardly turned stiffened lips on the outer distal edge of each leg, whereas the tracks do not. The tracks are dimensioned widthwise to fit over the ends of the studs, and the stud and track members are used to frame wall sections. The same basic shapes in wider and heavier gauge sizes are also used for floor framing sections. Both shapes are also used to assemble roof and other truss members of considerable spanning and load carrying capabilities.
Traditional cold roll forming devices consist of sets of two driven shafts positioned one above and one below a metal sheet passing through the device. Mounted on these shafts are roll elements whose profile has been machined to bend or form a strip of flat metal as it passes between the tightly spaced roll contours. This set of shafts, rolls and the mechanism that drives them is referred to as a roll pass. A roll former will consist of a number of such roll passes mounted in a flat steel base with all passes being mounted in a straight line, and with all shafts in parallel with each other. The profile of each set of rolls in each succeeding pass is designed to gradually change the cross section of the initially flat metal strip fed into the machine, into the final desired shape as it passes through the sets of rolls. The number of passes required will vary with the complexity of the shape being formed as well as the type of material, its thickness and physical properties.
Typically, the lower shaft is in a fixed position and is non-adjustable vertically. The upper shaft is typically vertically adjustable, usually having compression springs mounted between the bearing blocks of the upper and lower shafts which are sufficiently strong so as to not only support the weight of the upper shaft and its rolls, but to also hold it firmly against adjustment screws which limited the extent the shaft and its roll can move upwardly. The design and machining of the rolls is done in a manner to allow a particular gauge or thickness of metal strip to pass between them. This space or clearance between the rolls is usually a compromise to allow clearance for more than one gauge to pass through the machine by making adjustment of the screws located above each bearing of the upper shaft.
The clearance or space between the upper and lower roll contours must be sufficient to allow the rolls to slip against the metal strip being formed as there is obviously only one point on the circumference of each roll, called the drive point, at which the metal strip and the surface of a given roll can be traveling at the same speed. This point will vary with each set of rolls in each pass, in that the rolls not only form the metal strip but also function to drive the strip through the machine. The balance of the metal strip and roll surfaces are sliding in relationship to each other.
To successfully roll form a finished shape, the metal's yield strength must not be exceeded as the metal is formed by the rolls. Otherwise, strains can be induced at the points where it is exceeded which in turn can result in stretched metal with residual stresses that can distort, twist and curve the shape of the finished part. Assuming that the roll tooling has been properly designed to avoid this particular problem, there are a number of other factors which still cause problems in existing roll forming technology. The rolls in a typical roll forming device are typically positioned firmly in a fixed position against a shoulder on each shaft. Good tooling design must assume the space or clearance between the two rolls remains constant. However, there is no such thing as absolute perfection in either the roll former or it's roll tooling, nor in the metal strips which are to be passed through the machine.
There are a number of tooling variables that may be the source of other problems. Drive shafts which are less than absolutely straight, or rolls that are not absolutely concentric or not uniformly fitted to their drive shafts, and similar variations from perfection, can cause the rolls to lope during rotation. This may vary the design spacing between the rolls, thus alternately squeezing and inducing stresses in the metal as it passes through the machine. Other similar machine and tooling variables can also be cited. The degree of these variables in a machine and its tooling can increase during the operating life of both because of wear and strains that are either induced or relieved through production usage.
There may also be metal strip variables. Perfection in the metal strip being roll formed is also not likely. An article from the October issue, 2002, of The Fabricator magazine, outlines the reality of the variables inherent with present day state of the art metal strip roll form production. These strip variables coupled with machine and tooling variations outlined above, combined to induce stresses during roll forming which can seriously affect the quality of the finished formed parts. Thus, there remains a need in the art for an apparatus which can roll form such metal components for wall structures as well as assembling wall structures from such components and which overcomes the numerous aforementioned problems inherent in the existing technology. The present invention addresses and solves these particular problems in the art.